Bonding Between Atoms

Why do Atoms Form Bonds? To get a stable octet of valence electrons. Called a “noble gas configuration” IONIC BOND = valence e- transferred COVALENT BOND = valence e- shared

Changes in Energy Energy is released when bonds form. (exothermic) Results in lower energy, more stability Know example…

Lewis Dot Diagrams of Atoms Show valence electrons that are involved in bonding

Lewis Dot Diagrams of Ions Positive Ions (cations): lose outer shell valence to get stable octet. Negative Ions (anions): gain electrons to complete outer shell octet.

Ionic Bonding Happens between metals and nonmetals Forming Table Salt :6 minutes http://science360.gov/obj/video/c8b6ed58-5791-4fc1-8619-62fd8d99d9d0/atoms-bond-ionic-bonds

Atoms Become Ions Metals Lose Electrons: Ex: Mg is 2-8-2 Loses 2 electrons to become Mg+2 2-8 Nonmetals Gain Electrons: usually take top (-) charge become (–) ion Ex: Cl is 2-8-7 Gains 1 electron to become Cl-1 2-8-8

Electron Transfer As ions form, an exchange or transfer of electrons happens. Lithium (metal) 2-1 Fluorine (nonmetal) 2-7

Electronegativity Difference Atoms in ionic compounds have large differences in their EN values ( > 1.7) The greater the EN difference, the more “Ionic Character”.

Ex: EN Values Metal Na = 0.9 Nonmetal Cl = 3.2 Nonmetal with higher EN “takes” electron(s) from metal

Positively and negatively charged ions form and attract each other due to OPPOSITE CHARGES. Attraction forms an IONIC BOND - ion + ion

Ionic compounds have a uniform crystalline lattice structure.

Can you identify an ionic compound from a covalent?

Drawing Lewis Dot Diagrams of Ionic Compounds Do Page 7 in Bonding Packet

Writing Ionic Formulas

Ionic Compounds are Neutral Subscripts show ratio of ions Total positive and negative charges must balance so the compound is electrically neutral.

Writing Neutral Ionic Formulas Write symbols of elements Write the charges Criss-Cross charges if necessary to balance the formula Put parenthesis around polyatomic ions if more than one in formula Simplify if needed. Tutorial on writing ionic formulas 9 min http://www.youtube.com/watch?v=vscoYh6m46M

Stock System for Naming Ionic Compounds Binary: Contain ions of 2 elements Ex: MgCl2, Al2O3, NaCl

Naming Binary Ionics Name metal Name nonmetal with “-ide” ending. Ex: NaCl, MgBr2, CaO, Al2S3

Ternary: Contain 3 elements Polyatomic ion present. Elements inside the polyatomic ion are covalently bonded (all nonmetals). Thus these compounds contain both ionic and covalent bonds!! Ex: NaNO3, Ca3(PO4)2, NH4Cl

Naming Ternary Ionics (with polyatomic) Name Metal Name polyatomic ion If two polyatomics, name them both

When to Use a Roman Numeral Roman numerals are used when the metal can have more than one possible charge. Roman numeral indicates the charge the metal takes in that compound and must be indicated in the name Ex: NiBr2 Nickel II Bromide NiBr3 Nickel III Bromide

Crash Course Chemistry: Nomenclature (only watch first 6 minutes, skip section on naming acids for now) http://www.youtube.com/watch?v=mlRhLicNo8Q

Properties of Ionic Compounds

High Melting Point Attraction between the ions is very strong. Requires a lot of heat energy to separate ions and make solid crystal melt.

Solubility in Water Most ionics will dissolve in water, or be “soluble”. When dissolved in water they are “aqueous” Ex: NaCl (aq)

Water is a “polar molecule”. Acts like a magnet to pull ions apart and into solution. Ions are now “dissociated” or “hydrated” ions. http://youtu.be/EBfGcTAJF4o

Conductivity Ionic compounds conduct when ions are “mobile” or free to move about.

Conductivity Ionic compounds conduct when: Molten (melted/liquid) (l) Aqueous (aq) Note: They DO NOT conduct when solid as the ions are locked in place.

Dancing Queen: Song about Ionic vs Covalent Bonding http://www.youtube.com/watch?v=QIfTT-_-xLo Crash Course: Atomic Hookups http://www.youtube.com/watch?v=QXT4OVM4vXI